The present invention relates to a corded earplug and specifically to a method for making such a corded earplug.
In the prior art, corded earplugs are generally made by initially making an earplug by any conventional technique. The earplugs are either produced with an elongated opening at one end an elongated opening is made at hole at one end of the earplug after it has been produced. An adhesive is then applied to the opening and one end of a cord is inserted into the elongated opening during the short time that the adhesive is liquid. This adhesive then bonds the cord within the opening at one end of the earplug and generally a pair of such earplugs are located at opposite ends of the cord. This produces the conventional type of corded earplug, which includes a number of additional steps after the earplugs are produced.
The difficulty with prior art corded earplugs is that it is difficult to insert the cord into the opening during the short period of time that the adhesive is liquid. In addition this method of attaching the cord to the earplug can result in a bond which is completely dependent on the adhesive and therefore may not be very strong. It would therefore be desirable to provide for a method of attaching a cord to an earplug using a method, which is simpler than the prior art and also produces strong bonding between the cord and the earplug.
The present invention is directed to a corded earplug, and specifically to a method of making such a corded earplug, which provides for inserting the ends of the cord into openings in an injection mold. The mold is with plastic and with this occurring either before or after the mold is closed. For example the plastic can be injected and then the mold is quickly closed to have the plastic formed in the mold around the ends of the cord. Alternatively, the plastic may be injected into the mold after the cord ends are inserted and the mold closed.
Because of this technique, the molded plastic is formed around the cord itself to produce a very strong bond to the cord. In some instances when the cord material and the plastic material are similar in nature the bond can be very intimate since as the plastic sets up in the mold and bonds on a molecular basis to the cord. In other instances when the materials are different, such as when the molded earplug is a foam material, as the foam material foams it will lock tightly onto cord ends. In all instances since the molding is a hot process this tends to soften the cord again providing for an intimate bond between the cord and the earplug.
The present invention is disclosed with reference to two types of earplugs, one of a foam molded type and the other of an earplug made out of a resilient elastomeric rubber-like material similar in nature to the cord itself. The methods for making these two types of corded earplugs both incorporate the use of the ends of the cords being inserted into a mold and with the earplug then molded around the cord end. One embodiment provides for the entire earplug to be molded at the same time. The second embodiment discloses molding a portion of an earplug around the cord and with the portion of the earplug then incorporated with a flanged portion to produce a particular type of flanged earplug.